1. Field of the Invention
The present invention relates to inertial energy storage devices, and more particularly to a superflywheel energy storage device which is capable of compensating for the many destructive forces generated by rotation of the flywheel at high speeds.
2. Description of the Contemporary and/or Prior Art
The storage energy density of flywheel structures has been greatly increased during the last decade through the employment of filamentary materials, the use of which has permitted various previously unknown designs. These anisotropic and isotropic filamentary materials such as carbon, fiberglass, Metglas, or a DuPont fiber known as Kevlar, all have strength to density properties significantly greater than that of steel. As a result, useful storage energy density levels, which are obtainable by winding these anisotropic materials into flywheel rims, far exceed storage energy density levels of previously configured flywheels.
Flywheel rims constructed of windings of anisotropic materials are most efficient if the mass of the hub and connection between the hub and the rim is reduced to a minimum with the bulk of the mass of the flywheel being located at the rim. As these wound rim flywheels are spun to higher and higher speeds to increase energy storage, the tensile strength of the means employed to connect the wound rim to a hub is eventually exceeded and flywheel failure immediately follows. In an attempt to most effectively mount a flywheel rim to a hub, various spokes or other mountings have been suggested both in the prior art and as parallel developments to the present invention. The present invention affords significant improvements over configurations presently known and also provides for a simply constructed structure which does not require elaborate, expensive, or complicated fabrication techniques and methods.
The problem of expansion of a wound filament rotor rim of a flywheel has been recognized in U.S. Pat. Nos. 1,365,473 issued to W. L. R. Emmet on Jan. 11, 1921 and 1,426,339 issued to E. A. Sperry on Aug. 15, 1922. Both of these patents teach mechanisms which provide for moderate expansion between spoke structures that are fixedly secured to flywheel hubs and the flywheel rim. These apparatuses teach movable joints between the spoke means and the rims thereof that engage the entire circumference of the inner portion of the rims to permit a minimal degree of expansion of the rim without failure of the spoke means. While such joints may have been adequate for low energy storage flywheels at slow rotational speeds, these structures are wholly inadequate for use with high energy level storage rims which store energy at high rotational speeds. In fact, these inventions were designed for use with wound metal rims which are well known in the art as having energy storage levels which in no way approach those of anisotropic filamentary materials which are wound into flywheel rims.
U.S. Pat. No. 3,724,288 issued to M. Jabukowski on Apr. 3, 1973 shows a high energy storage flywheel which is very similar in appearance to a bicycle wheel. A rim which includes a form having a substantially U-shaped cross section is provided and an anisotropic material is wound circumferentially within the substantially U-shaped area. The form is then attached to a hub by a plurality of discrete spokes with each of the spokes being secured on one end thereof to the form by bicycle-wheel type sleeve nuts with the other end of the spokes being secured to apertures in the hub. No means are shown or suggested for constraining the winding within the U-shaped area of the form and if this structure were spun at the speeds contemplated by the present invention, failure of the rim either by breaking or cracking of the sleeve nuts and/or separation of the winding from the form would occur at rather low energy storage levels. Some degree of axial stability is provided by extension of the discrete spokes from the outer surfaces of the hub to the central portion of the form around the circumference thereof. The present invention avoids the use of discrete spokes and connectors which are inherently weaker than a continuous spoke winding and provides for a greater degree of axial stability by having spokes crossing from one surface of a hub to the opposed surface of a rim without terminating midway between the surfaces of the rim as taught by Jabukowski.
U.S. Pat. No. 3,964,341 issued to D. W. Rabenhorst on June 22, 1976, teaches a rotary energy storage device which teaches multi-ring and discrete ring filament rotor windings. These windings are secured in various manners to a hub. This is primarily accomplished by radial wraps which are secured to a spoke-like member and extend around the peripheral edge of the flywheel winding.
U.S. Pat. No. 4,036,080 issued to J. A. Friedericy et al on July 19, 1977 discloses a multi-rim flywheel which comprises a plurality of discrete rings which are mounted on a spoke member in a subcircular fashion. Because of the subcircularity of the ring members, the rings are maintained through friction on the hub which includes a plurality of spiders. This structure relies closely on matching and interrelating the circumferences of the rings to supply the proper frictional engagement. Each of the rings engages adjacent rings along the entire adjacent circumferential surfaces thereof and therefore the forces generated upon rotation of the flywheel are not directed through a desired path as taught by the present invention.
The advantages of using a single filament for forming spoke means for affixing a flywheel rim to a hub has been recognized in U.S. Pat. No. 3,977,273 issued to A. O. G. Ernst et al on Aug. 31, 1976. Ernst proposes a flywheel which comprises a hub and a rim wherein a filament is wrapped around the exterior of the rim and around the hub in a repeating pattern so that a fabric is woven into a sheet which covers the entire outer surfaces of the rim and encloses the same therein. Therefore, this sheet essentially forms a solid tapered shell. Since the filament winding of the shell is constantly wound upon itself adjacent to the hub, the area adjacent the hub becomes prohibitively thick and places mass in an inefficient position adjacent to the hub. The shell goes around the entire outside of the rim, and therefore the rim bears directly upon and is constrained by the shell, severely limiting necessary radial expansion of the circumferential fibers of the rim. Aside from the foregoing limitations of Ernst, axial stability is minimal since shifting of the rim relative to the hub is only controlled by contact between the outer surface of the rim and the inner surface of the sheet.
U.S. Pat. No. 4,123,949 issued to Knight Jr. et al on Nov. 7, 1978 teaches an inertial energy storage device wherein a circumferentially wound resin impregnated filament material is employed to form a flywheel rim. The flywheel rim is secured to a hub by a plurality of discrete filament band sets which wrap around the outer surface of the rim and engage the outer surface of the hub. The outer surface of the hub provides a plurality of protrusions for capturing portions of the band sets. These band sets are taught to be wound with a uniform stress so that they can accommodate the allegedly uniform stress created by the rim during acceleration and deceleration of the flywheel. Unfortunately, the premise that uniform stress will be provided is not sound unless meticulous balancing and forming of the rim is undertaken. This balancing is both time-consuming and costly. In addition, the protrusions on the hub may well look like knife edges at high rotational speeds and can possibly cause failure of the band sets which will cause failure of the entire flywheel. Axial stability is not provided for except to the degree that the band sets can stabilize the rim through their outer wrapping about the hub. In addition, since the band sets which serve as spokes contact the outer surfaces of the rim, all the forces at these locations which want to break the rim during rotation are concentrated directly on the band sets. The crisscross windings of the filament of the present invention forming the spokes thereof provide greater axial stability than the band sets of Knight. In addition, the configuration of the present invention, which employs an inner ring and an outer rim, fixedly secured together at discrete locations, more advantageously distributes the load created by the rotating rim than the band sets of Knight.
The present invention overcomes the shortcomings associated with the prior art and other contemporarily developed flywheels by providing a flywheel which does not suffer from axial instability, does not require overly precise manufacture, and which transfers the stresses from the rim thereof to the hub thereof through spoke means over a more advantageous path than has been suggested in the previously discussed references.